1. Field of the Invention
The invention relates to a support for a large vertical axis wind turbine (VAWT).
2. Description of the Related Art
In the invention, large vertical axis wind turbines refer to those with output power more than 50 kW.
Conventional supports of large vertical axis wind turbines, as shown in FIG. 1, include a platform 2 disposed on a tower frame 1 for installing and fixing wind turbines. Several parts 3, such as generators, connectors, brakes, and transmissions, are installed on the platform 2. The tower frame 1 supports a vertical central axis 4 and a vertical axis windmill consisting of blades 6 and supporting arms 5. The tower frame 1 is hollow in structure. The vertical central axis 4 is solid or thick-walled and hollow. The supporting arm 5 is hollow in structure.
Subject to multiple factors such as supports, the power of conventional VAWTs is generally low. To maintain the stability of conventional supports in strong wind (for example, at wind velocity of 60 m/s), the tower frame and vertical central axis must be made very strong. Furthermore, with the increase of the windmill diameter, the diameter of the tower frame and the vertical central axis must be increased proportionally. However, due to the limit of industrial equipment and cost, the development of larger VAWT products is affected.
For example, assuming a VAWT has a solid vertical central axis and a windmill thereof is 50 m in diameter and 40 m in height. Under a safe wind velocity of 60 m/s, the lateral wind force exerted on the windmill is approximately 2700 KN. To prevent the wind turbine from being damaged by wind at 60 m/s, the vertical central axis need be designed about 25 m in length, approx. 1.5 m in diameter, and nearly 350 t in weight. Although the strength of the supports is enough, the rigidity thereof is insufficient. Likewise, if the vertical central axis is thick-walled and hollow, it should be approx. 3.5 m in diameter and a hundred tons in weight. Moreover, the larger the diameter of the central axis, the larger the diameter of bearings, thus significantly increasing cost. For a tower frame, even it is only 25 m in height, the maximum bending moment at the bottom is approx. 1.26×105 KN·m, the diameter of the tower frame needs approx. 6 m or larger, weighing about 150 t. In addition, the base of the tower frame need be enlarged accordingly, thus greatly increasing the cost of large VAWTs.